1. Field of the Invention
The present invention relates to a vacuum insulated refrigerator cabinet comprising a substantially gas-tight container that is filled with a substantially porous core and a gas-storage container that communicates with said container and is filled with a gas adsorbent material. A vacuum insulated refrigerator cabinet of this kind is disclosed by EP-A-860669.
With the term “refrigerator” we mean every kind of domestic appliance in which the inside temperature is lower than room temperature, i.e. domestic refrigerators, vertical freezers, chest freezer or the like.
2. Description of the Related Art
The good insulation-capabilities of different vacuum-insulation materials (fibre, foam or powder-based) are well known in the field of refrigeration and have been improved significantly in the last decade. Despite of these improvements and the increasing demand for reduced electricity consumption, an industrial production of vacuum-insulated refrigerators for domestic private use has not been started yet, although much development work has been invested.
The main problem is to sustain the vacuum for times of 10–15 years (usual life of a domestic appliance) without increasing too much the production cost of the product. While the traditional method, which consists in welding “vacuum-tight” structures (mostly of stainless steel), is very expensive (both in process and especially in material cost aspects), the refrigerator cabinets produced with the more cost-effective system which makes use of plastic liners (with or without anti-diffusion claddings) have a limited lifetime and therefore they are not yet in production. The solution disclosed in the above mentioned EP-A-860669 does not mostly guarantee low-pressure levels in the gas-tight container for substantially the entire life of the refrigerator. The alternative solution of providing a refrigerator with a vacuum pump running almost continuously, as shown in EP-A-587546, does increase too much the overall energy consumption of the refrigerator (in other words what it is saved in terms of decrease of heat transfer through the wall of the refrigerator is lost in running the vacuum pump). Such known way to maintain a vacuum in the wall of a refrigerator cabinet uses a pump to periodically recover the required vacuum that may be degraded by permeation of gasses and water vapor. Small, low cost mechanical pumps will not be able to reach the vacuum levels required to achieve acceptable insulating values. Small, low cost, mechanical pumps can evacuate down to a range of 20 to 200 mbar quite rapidly. However, most vacuum insulation fillers require vacuums below this range. Some open celled foam fillers require a vacuum lower than 0.1 mbar to reach the kind of thermal conductivities desired.